There is increasing research and development into devices and methods for endoluminal treatment of or in small vessels, particularly the cerebral vessels. Such treatments can avoid the necessity for open surgical procedures, which can be traumatic, involve significant patient risk and require lengthy hospitalisation and recovery times. There are many treatments which can be performed on such vessels by endoluminal procedures, including just as examples, treatment of aneurysms, opening of vessels, implantation of filters, administration of medicaments, as well as delivery of diagnostic tools.
Small vessels, especially cerebral vessels, are particularly sensitive and as a result are prone to going into spasm should they be traumatised in any way. When a vessel begins to spasm it can close, preventing further movement of any endoluminal medical assembly in the vessel. Vessel spasm can occur when the vessels are touched by a hard substance, such as a part of an introducer assembly. It is not always practicable to make such assemblies of a soft material as they need to have a certain rigidity in order to have adequate pushability through a patient's vasculature and also to protect the components of the assembly. There have been suggestions as to how to soften such assemblies, but often this is after their implantation into a patient, and thus after they have been pushed through the patient's vasculature. Such solutions to not avoid the risk of causing vessel spasm.
As a result, and in order to maintain adequate pushability of the assembly, it has been known to limit the size of the introducer assemblies, so that they are significantly smaller in diameter than the diameter of the vessel. However, such diameter restriction limits the size of devices which can be introduced into these vessels and can limit the range of treatments or of diagnosis which can be performed.
Examples of prior art medical catheters and introducer assemblies can be found in US-2004/0059290, U.S. Pat. No. 4,976,703, U.S. Pat. No. 4,790,817, U.S. Pat. No. 7,651,488, US-2008/0228168 and WO-96/27405, the contents of which are incorporated by reference.